From the Departments of Medicine and Pediatrics (Dr Flume), Medical University of South Carolina, Charleston, SC; the University of Utah (Dr Liou), Salt Lake City, UT; the Department of Pediatrics (Dr Borowitz), State University of New York at Buffalo, Buffalo, NY; Vertex Pharmaceuticals Incorporated (Drs Li, Yen, and Ordoñez), Cambridge, MA; and the Divisions of Biomedical Research and Pediatric Pulmonology (Dr Geller), Nemours Children’s Clinic, Orlando, FL.

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Funding/Support: The DISCOVER study is sponsored by Vertex Pharmaceuticals Incorporated. This research was supported by the Cystic Fibrosis Foundation to the Women and Children’s Hospital of Buffalo [Grant BOROWI03CS0] and to the Medical University of South Carolina [Grant C104-TDC10Y].

Abstract

Background:Ivacaftor (VX-770) is a cystic fibrosis transmembrane conductance regulator (CFTR) potentiator that was approved in the United States for the treatment of cystic fibrosis (CF) in patients ≥ 6 years of age who have a G551D mutation; however, the most prevalent disease-causing CFTR mutation, F508del, causes a different functional defect. The objectives of this study were to evaluate the safety of ivacaftor in a larger population and for a longer time period than tested previously and to assess the efficacy of ivacaftor in subjects with CF who are homozygous for F508del-CFTR.

Methods:This was a phase 2 study with a 16-week randomized (4:1), double-blind, placebo-controlled period (part A) and an open-label extension (part B) for subjects who met prespecified criteria.

Results:Part A: The safety profile of ivacaftor was comparable to that of the placebo. The overall adverse event frequency was similar in the ivacaftor (87.5%) and placebo (89.3%) groups through 16 weeks. The difference in the change of FEV1 % predicted from baseline through week 16 (primary end point) between the ivacaftor and placebo groups was 1.7% (P = .15). Sweat chloride, a biomarker of CFTR activity, showed a small reduction in the ivacaftor vs placebo groups of −2.9 mmol/L (P = .04) from baseline through week 16. Part B: No new safety signals were identified. The changes in FEV1 or sweat chloride in part A were not sustained with ivacaftor treatment from week 16 to week 40.

Conclusions:These results expand the safety information for ivacaftor and support its continued evaluation. Lack of a clinical effect suggests that a CFTR potentiator alone is not an effective therapeutic approach for patients who have CF and are homozygous for F508del-CFTR.

Return to: Ivacaftor in Subjects With Cystic Fibrosis Who Are Homozygous for the F508del-CFTR Mutation

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